Device for interchanging suction pipettes

ABSTRACT

The invention relates to a device for interchanging suction pipettes which can be removed from a magazine and coupled to a fitting head of a fitting device and detached from the fitting head and deposited in the magazine. The fitting head has, on its side facing the magazine, a motor on whose driven shaft a star-shaped part and a latching plate are mounted. The latching plate has at least one nub ( 121 ) which, after insertion of the star-shaped part into a star-shaped cutout in the suction pipette held in the magazine and after rotation of the star-shaped part and the latching plate into a locking position, engages in a notch, and which, on insertion of a suction pipette held on the star-shaped part into the magazine, can be moved out of the notch. The magazine has, on the side facing the fitting head, a sliding ring which is arranged in a rotationally fixed manner in the magazine and into which the suction pipette can be inserted in such a manner that the star-shaped latching plate comes to rest with its outer edges on the sliding ring where it is raised resiliently away from the star-shaped part, so that the nub is situated above that surface of the suction pipette which faces the fitting head.

FIELD OF THE INVENTION

[0001] The present invention relates to a device for interchanging suction pipettes in accordance with the preamble of patent claim 1.

[0002] It is known to couple suction pipettes, after removal from a magazine, onto a fitting head for the automatic fitting of printed circuit boards with components and, conversely, to return them back into the magazine from the fitting head after a fitting operation. In this case, the pipettes which are provided in the magazine are received by a sleeve in that a star-shaped part of the sleeve is connected by rotation in an interlocking manner to the intersecting point of the pipette and is secured by a latching plate. This process is explained in greater detail in conjunction with FIG. 1 in which a fitting head is denoted by 3. A rotary motor for the fitting head 3 is denoted here by 14. A star-shaped latching plate 12 and a star-shaped part 4 are arranged aligned with respect to each other on the driven shaft of the rotary motor 14.

[0003] During the coupling-on of the pipette, the star-shaped part, which has a longitudinal passage 18, is inserted, by exerting a pressure in the direction of the pipette (Z axis), into a star-shaped cutout facing it in the pipette held in a magazine, in which case the abovementioned, star-shaped cutout is situated in that surface of the pipette which faces the fitting head. By rotation of the star-shaped part 4 in the circumferential direction of the pipette held firmly in the magazine, the star-shaped part 4 is locked in a bayonet-like manner to the pipette, in which case outer edges of the projection of the star-shaped part pass under the abovementioned, star-shaped cutout in the wall part fitting over it in the circumferential direction. This corresponds to the locking position between the star-shaped part 4 and the pipette. The star-shaped, resilient latching plate which is fastened congruently to the star-shaped part 4 has a projection or a nub which faces the pipette and, on rotation of the star-shaped part 4 together with the latching plate into the locking position, slides over an arc of a circle outside the star-shaped cutout of the pipette until it enters, in the locking position, into a notch which is situated on the abovementioned arc of a circle. This has the effect of maintaining the locking position. An annular seal, which is provided on the star-shaped part, ensures a tight connection between the abovementioned hole in the star-shaped part 4 and the pipette, so that a vacuum can be applied to the pipette via the hole in the star-shaped part 4.

[0004] One problem of such a locking arrangement between the star-shaped part and the pipette is that the force which is to be applied for detaching the star-shaped part from the pipette when the latter is deposited in the magazine and which is required in order to overcome the latching force of the nub of the latching plate, so as to move the nub out of the notch in the circumferential direction, is relatively large, even if the notch has sloping surfaces. The moment required for rotating the star-shaped part in relation to the pipette therefore has to be relatively large. Conversely, if a certain, minimum moment is specified, the retaining force is defined by this moment. A further disadvantage is that the wear to the notch and nub is relatively great, and so the service life in particular of the pipettes is limited.

[0005] The object of the present invention is to provide a device with which an interchange of suction pipettes on a fitting head can be carried out relatively reliably with comparatively small coupling and uncoupling moments.

[0006] This object is achieved by a device for interchanging suction pipettes having the features of patent claim 1.

[0007] The essential advantage of the present invention resides in the fact that a relatively small moment is sufficient for rotating the star-shaped part into the locking position when a pipette is picked up out of a magazine, since unlike in the prior art, the latching plate does not slide on the pipette itself, but on a special sliding ring having a low coefficient of friction. During the latching and unlatching process, the nub of the star-shaped latching plate does not have to overcome in the circumferential direction the slopes of the notch of the pipette, because the nub which slides on the sliding ring having a small coefficient of friction is, after the locking position is reached and the latching plate relieved of load, inserted in the Z axis from above from the sliding ring gently into the notch. Conversely, on insertion of the pipette into a magazine and with the latching plate being pressed down, the nub is moved upward in the Z axis out of the notch because the latching plate comes to rest on the sliding ring. As a result, the moments occurring during the latching and unlatching of the nub can advantageously be reduced by up to a factor of 6.

[0008] In an advantageous manner, the retaining force which exists between the pipette and star-shaped part can be increased by greater prestressing of the latching plate. In addition, according to a further essential advantage of the invention, there is no wear in the region of the notch.

[0009] The low coupling and uncoupling moments advantageously enable a motor which is less powerful in terms of torque and is therefore lighter in weight to be used. This is of great significance, since the star-shaped part and the latching plate and the pipette connected thereto in the locking position fit directly on the shaft of the motor and the motor therefore has to be accelerated directly in the direction of the Z axis during the fitting process. In order, when placing components on a printed circuit board, to bring about small placing-on forces, the weight of the motor has therefore to be small. By means of the invention, a placing-on force of, for example, 0.5 N, which is the lowest which is required, can be achieved with a relatively high fitting speed.

[0010] In an advantageous manner, the present device is designed in such a manner that it can also be used in conjunction with already known pipettes. A new design for the pipettes is therefore not required.

[0011] Advantageous refinements of the invention emerge from the subclaims.

[0012] The inventions and refinements thereof are explained in more detail below in conjunction with the figures, in which:

[0013]FIG. 1 shows, in a perspective illustration, a known fitting head having means for interchanging suction pipettes;

[0014]FIG. 2 shows a section through a device according to the invention, the star-shaped part being arranged in the locking position;

[0015]FIG. 3 shows a plan view from above of a magazine;

[0016]FIG. 4 shows a plan view from above of the latching plate fitting on the sliding ring;

[0017]FIG. 5 shows a section through a pipette, and

[0018]FIG. 6 shows a view of the pipette from the fitting head.

[0019] In FIG. 2, a magazine in which a pipette 2 is arranged is denoted by 1. In the present device, it is of decisive importance that a sliding ring 8 is arranged in the magazine 1, into which sliding ring the pipette 2 can be inserted. For this purpose, the sliding ring 8 preferably has a lower, radially inwardly protruding flange 81 on which the outer edge 21 of the pipette 2 rests. The sliding ring 8 furthermore preferably has an upper, radially outwardly protruding flange 82 which rests on the upper side of the magazine 1. The magazine 1 expediently has the shape of a square housing with a space 16 which serves to accommodate the lower region of the pipette 2. The interior 16 widens outward via a step 11 on which the lower flange 81 and the sliding ring 8 rests. A respective retaining spring 6 is arranged in two radial incisions 15 provided on diametrical sides of the magazine 1, said retaining spring being of approximately U-shaped design and its lower leg being fastened below the step 11 to the bottom of the incision 15 particularly with the aid of the head of a screw 13. Starting from the lower leg which runs radially outward in the incision 15, the rataining spring 6 runs in a curved manner to an upper leg which runs radially inward in the incision 15 and whose free end region is guided through a radial cutout 83 in the sliding ring 8. As it does so, the retaining spring 6 uses its spring force to pull the sliding ring 8 in the direction of the step 11.

[0020] In FIG. 3, the sliding ring 8 and the flanges 81, 82 are illustrated as seen from above by dash-dotted lines.

[0021] The star-shaped latching-in plate 12, which preferably consists of spring steel, has, on a projection protruding outward in a star-shaped manner, a nub 121 which protrudes in the direction of the sliding ring 8 and, in a locking position, latches into the notch 10 which is situated in that surface of the pipette 2 which faces the latching plate 12. The view of the pipette 2 from the motor 14 is illustrated in FIG. 6. FIG. 5 shows a section through the pipette 2. The star-shaped cutout for accommodating the star-shaped part 4 is denoted by 22 and the wall parts mentioned at the beginning are denoted by 23. The radially extending notch 10 is situated in one wall part 23 (in the left-hand wall part 23 in FIGS. 5 and 6), on the side which faces the star-shaped part 4. Situated on the rear sides of a wall part 23, as seen in the rotational direction to the locking position, is a stop 24 for the corresponding edge of the projections of the star-shaped part 4 for securing the locking position.

[0022] So that the pipette 2 can be inserted into the sliding ring 8 and removed therefrom, it has incisions 26 on the outside which are diametrically opposite each other and through which those ends of the upper legs of the retaining springs 6 which protrude radially inward over the sliding ring 4 can pass, on insertion of the pipette 2 into the sliding ring 4 and on removal of the pipette 2 from the sliding ring 4.

[0023] The latching plate 12 is dimensioned in such a manner that it protrudes outward over the circumference of a pipette 2 which is to be picked up and therefore, on entry of the star-shaped part 4 into the star-shaped recess 22, comes to rest on the upper flange 82 of the sliding ring 8 and is raised in the Z axis counter to its spring force sufficiently for the nub 121 to be situated above the plane of that surface of the pipette 2 in which the notch 10 is arranged. This has the effect that when the star-shaped part 4 and the latching plate 12 are rotated (in the clockwise direction in FIG. 6), the latching plate 12 slides with its outer edges 21 on the sliding ring 8 until the nub 121 is situated in the locking position above the notch 10. When the sleeve 2 and the star-shaped part 4 are raised, the resiliently prestressed latching plate 12 relaxes and the nub 121 enters from above in the Z axis into the notch 10.

[0024] In order to enable a particularly friction-free rotation of the latching plate 12 on the sliding ring, the sliding ring 8 is preferably manufactured from a readily slideable plastic material which has a very low coefficient of friction. As an alternative or in addition, the latching plate 12 can be coated, at least in its regions which rest on the sliding ring 8, with a material of a small coefficient of friction. A low moment is therefore sufficient for rotating the star-shaped part 4 and the latching plate 12, since the latching plate 12, unlike in the prior art outlined at the beginning, does not slide with relatively great friction on the pipette itself, but slides on the sliding ring 8 having a low coefficient of friction. Since the nub 121 executes a vertical movement during the latching and unlatching process, it does not have to overcome the slopes of the notch, as is required in the prior art.

[0025] When the pipette 2 is deposited in the sliding ring 8 of the magazine 1 (in which case the free ends of the upper legs of the retaining springs 6 enter into the incisions 26), the latching plate 12 again comes to rest on the flange 82 of the sliding ring 8 and in the process the nub 121 is raised upward in the Z axis out of the notch 10, in which case the latching plate 12 is prestressed counter to its spring force. During subsequent rotation of the star-shaped part 4 and the latching plate 12 out of the locking position (rotation in FIG. 6 anticlockwise), the latching plate again slides on the sliding ring 8 in a manner low in friction until the star-shaped part 4 can be passed out of the region of the wall parts 23 and moved away from the magazine 1 in the direction of the Z axis, when the ends of the upper legs of the retaining springs 6 are aligned with respect to the incisions 26. 

1. A device for interchanging suction pipettes which can be removed from a magazine and coupled to a fitting head of a fitting device and detached from the fitting head and deposited in the magazine the fitting head having, on its side which faces the magazine a motor on whose driven shaft a star-shaped part and a latching plate are mounted, the latching plate having at least one nub which, after insertion of the star-shaped part into a star-shaped cutout in the suction pipette held in the magazine and after rotation of the star-shaped part and the latching plate into a locking position, engages in a notch which is situated in that surface of the suction pipette which faces the fitting head and which nub, on insertion of a suction pipette held on the star-shaped part into the magazine can be moved out of the notch characterized in that the magazine has, on the side facing the fitting head a sliding ring which is arranged in a rotationally fixed manner in the magazine and into which the suction pipette can be inserted in such a manner that the star-shaped latching plate comes to rest with its outer edges on the sliding ring where it is raised resiliently away from the star-shaped part so that the nub is situated above that surface of the suction pipette which faces the fitting head and, after rotation of the star-shaped part and the latching plate into the locking position and after removal of the suction pipette from the sliding ring enters from above, when the latching plate is relaxed, into the notch and, when the star-shaped part enters into the sliding ring is raised, by prestressing and raising of the latching plate upward out of the notch.
 2. The device as claimed in claim 1, wherein the magazine has, on its side facing the fitting head a step for the support of a lower flange of the sliding ring which has an upper flange for the bearing of the outer edges, which flange rests on the edge region of a cutout in the magazine, said cutout accommodating the sliding ring.
 3. The device as claimed in claim 1, wherein the sliding consists of a plastic material having a low coefficient of friction.
 4. The device as claimed in claim 1, wherein the latching plate is coated, at least in its regions resting on the sliding ring, with a material of a small coefficient of friction.
 5. The device as claimed in claim 1, wherein the latching plate consists of spring steel.
 6. The device as claimed in claim 1, wherein the sliding ring is fastened to the magazine by at least one retaining spring.
 7. The device as claimed in claim 6, wherein the retaining spring is of U-shaped design and has a first leg which is held on the magazine, extends radially outward and runs in a curved manner with respect to the side of the fitting head and merges into a second leg which runs radially inward above the first leg, is guided through a radially extending incision in the magazine and whose free end region is guided through a cutout in the sliding ring.
 8. The device as claimed in claim 7, wherein the free end of the upper leg projects on the inside over the sliding ring and, on insertion of the suction pipette into the magazine and on removal of the suction pipette from the magazine, can be passed through an incision in the suction pipette.
 9. The device as claimed in claim 6, wherein two retaining springs are provided diametrically opposite each other in the magazine.
 10. The device as claimed in claim 1, wherein the suction pipette has, for the bayonet-like locking of the star-shaped part to the suction pipette, wall parts which protrude radially inward above the star-shaped cutout and under which the projections of the star-shaped part pass, on rotation of the star-shaped part into the locking position, and in that the notch is situated in that surface of a wall part which faces the fitting head.
 11. The device as claimed in claim 10, wherein the suction pipette has a stop restricting the rotational movement of the star-shaped part into the locking position.
 12. The device as claimed in claim 10, wherein the suction pipette has a further stop which ends the rotational movement of the star-shaped part out of the locking position in a position in which the retaining springs are aligned with respect to the slots in the suction pipette. 